Sidelink Scheduling in Unlicensed Spectrum via LBT Feedback
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Solution Overview
Problem
In unlicensed bands, the ambiguity between the gNB and the WTRU due to listen-before-talk (LBT) uncertainty leads to inefficient resource utilization in sidelink transmissions, especially for multi-slot scheduling where one LBT failure impacts multiple scheduled slots.
Innovation Solution
The proposed solution involves a method where a WTRU receives downlink control information (DCI) indicating a time window to initiate a channel occupancy time (COT) and performs LBT to access an unlicensed channel. After successful channel access, the WTRU transmits uplink control information (UCI) to the base station, indicating the successful channel access and COT starting time, and may suggest sharing the COT with other WTRUs based on buffer status and COT duration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the WTRU performs LBT to access unlicensed channel for sidelink transmission, then fair sharing of unlicensed spectrum is achieved, but resource utilization efficiency deteriorates due to LBT failure impacting multiple scheduled slots
Solution Approach 1:
The WTRU provides feedback to the gNB about its LBT outcome (success or failure) for each scheduled slot. This feedback mechanism allows the gNB to make informed scheduling decisions for retransmissions, allocating resources only when the WTRU successfully accesses the channel, thereby improving resource utilization efficiency while maintaining fair spectrum sharing through LBT
Solution Approach 2:
The scheduling approach transitions from static multi-slot scheduling to dynamic per-slot scheduling based on LBT outcomes. The gNB adjusts resource allocation dynamically according to real-time channel access success, allowing the system to adapt to unlicensed spectrum conditions and improve overall resource utilization while preserving the fairness benefits of LBT
2Reliability
If the gNB schedules multiple slots for sidelink transmission, then transmission reliability is improved, but resource utilization deteriorates when LBT failure occurs in unlicensed band
Solution Approach 1:
Instead of scheduling all slots upfront regardless of LBT outcomes, the gNB schedules only the necessary portion of transmissions based on actual channel access success. The feedback mechanism enables the gNB to allocate resources for retransmissions only when needed, avoiding excessive resource allocation and reducing energy wastage while maintaining transmission reliability
Solution Approach 2:
The system changes the scheduling parameter from fixed multi-slot allocation to variable per-slot allocation based on LBT success probability and feedback. This parameter adjustment allows the system to optimize resource utilization by allocating resources proportionally to actual transmission needs, reducing energy wastage while preserving reliability
3Productivity
If the WTRU initiates COT for long duration to avoid multiple LBTs, then channel access efficiency is improved, but gNB awareness of channel access status deteriorates for sidelink transmissions
Solution Approach 1:
The WTRU provides explicit feedback to the gNB about its LBT outcome and COT initiation status. This feedback includes information about whether the WTRU successfully accessed the channel and the duration of the initiated COT, maintaining gNB awareness despite the WTRU autonomously managing the COT for improved channel access efficiency
Solution Approach 2:
The gNB pre-configures the WTRU with COT duration parameters and scheduling information before the WTRU initiates the COT. This preliminary action allows the WTRU to autonomously manage the COT for efficient channel access while ensuring the gNB has advance knowledge of the expected COT duration and can plan subsequent resource allocations accordingly
Data Source
AI summary
A wireless transmit/receive unit (WTRU) may receive downlink control information (DCI) scheduling a sidelink (SL) grant that indicates a time window to initiate a channel occupancy time (COT). The WTRU may perform listen-before-talk (LBT) to access an SL unlicensed channel in an unlicensed band within the indicated time window to initiate the COT. After a successful channel access outcome of the performed LBT, the WTRU may transmit uplink control information (UCI) to a base station. The UCI may indicate the successful channel access outcome and a COT starting time within the indicated time window to initiate the COT. Also, the UCI may further indicate an intended number of transmissions by the WTRU in the COT. Moreover, the UCI may further indicate reserved sub-channels, reserved interlaces, or both, within the COT. Additionally, based on a buffer status and the COT starting time, the WTRU may determine whether to share the COT.